Valve members for use in internal combustion engines, particularly diesel engines, are expected to perform for long periods of time under rigorous conditions. Generally, the head portion, including the seat face and the combustion face of the valve member exposed to the combustion chamber, is required to resist a variety of factors including high temperature, high pressure, corrosion, fatigue, erosion and wear while the stem portion of the valve member is required to possess high strength, wear and fatigue characteristics at temperatures lower than the temperature to which the head portion combustion face is exposed.
Recently, efforts have been made to provide the head and stem portions with the properties described by controlling the microstructure of metallic compositions from which the valve member is made such that the head portion of the valve member is provided with a generally coarse grain size and the stem portion is provided with a generally fine grain size that is smaller than the coarse grain size of which an exemplary method is disclosed in U.S. Pat. No. 4,547,229 assigned to the assignee of the present invention and the disclosure of which is included herein by reference.
The aforementioned method, however, relies upon selective solution heat treatment to enlarge the grain size only in the head portion requiring expensive apparatus to shield the stem portion from the solution head treating temperature whereas the present invention is operative to use less expensive more conventional equipment to provide the microstructure grain size characteristics desired as well as providing the seat face of the head portion with improved resistance to wear.